Waste-to-Resources: Exploratory Investigation of Sludge Biochar after Adsorption of Heavy Metals for Cement Mortar Production

Abstract

The sludge biochar waste (NBC), which adsorbs zinc and copper, was used as the raw material, and its crushed (SBC) was used to prepare cement mortar instead of cement at different dosage (1~8%) and different firing temperatures (300~600°C) to study the mechanical strength and thermal insulation properties of different composite types of cement mortar materials. The findings revealed that NBC, prepared through pyrolysis at 500 ℃, exhibited the highest adsorption capacity and possessed excellent water separation capabilities; and the SBC thus prepared plays the role of filling in cementitious sand, which can offset the negative impact of the hydration reaction process of the competition between the heavy metals and Ca2+, and the mechanical strength of the cementitious sand specimens prepared at 5% dosage is the best, with the flexural and compressive strengths of 8.6 and 36.17 MPa, respectively. These values were significantly higher than those of the control group, which had strengths of 5.91 and 25.63 MPa. Furthermore, as the dosage of SBC increased, there was a notable enhancement in the specific heat capacity of the cement mortar, accompanied by a reduction in its thermal conductivity. This resulted in the composite material displaying improved thermal storage and insulation performance. The leaching test confirmed that the incorporation of biochar significantly enhances the immobilization of heavy metals (namely Cu, Zn, Cd, Cr, Pb, and Ni) in the mortar material, achieving an immobilization rate exceeding 99%.

Keywords: Biochar, Heavy metal, Construction mortar, Sequestration, Recycle